It is very hard to capture what mediation really means in a written description. At its simplest, mediation is a process where an independent person assists you to resolve a dispute. It is a profession, a service and a form of dispute resolution.
In many ways, on paper mediation is a science. You can study and train to become certified and accredited as a mediator. There are standards and there are benchmarks for best practice. Skilled mediators spend years learning and fine-tuning their craft and adding to their toolkit, through formal education and practical learning.